Water • is a tasteless, odourless, appearing colourless for naked eye substance that is essential to all known forms of life. • is a universal solvent. • seawater (97%) has salinity of minimum 3.5% (35grams of sodium chloride mostly per 1 litre of water). • freshwater (3%) contains less than 0.5parts per thousand dissolved salts. It is surface water (0.3%) in lakes, rivers and underground as groundwater. Majority of freshwater is frozen in glaciers and ice caps.
Chemical and physical properties of water (H2O) • Water strongly absorbs infrared radiation. This results in pure water appearing slightly blue. • Water is a very good solvent for hydrophilic (‘water loving’) substances. • Water sticks to itself (cohesion) because it is polar. • Water has a high surface tension caused by strong cohesion between water molecules
Water is able to move up narrow tube against the force of gravity (capillary action). Water is able to moderate Earth’s climate by buffering large swings of temperature as it has high heat capacity and high heat of vaporization. Freezing point. Ice floats on the water. Fresh water at standard atmospheric pressure is most dense at 3.98°C. This keeps deep water to remain warmer than shallow freezing water and this is how fish can survive freezing temperatures in the water. Chemical and physical properties of water (H2O)
Chemical and physical properties of water (H2O) • Triple point is a single combination of pressure and temperature at which pure liquid water, ice and water vapour can coexist in a stable equilibrium = 0.01°C and 611.73 pascals. • Any electrical conductivity observable in water are from ions dissolved in it.
Water purity refers to purity from: • toxins • microbes • pollutants
Drinking water (potable water) • Is fit for human consumption. • Must be pure from toxins, pollutants and microbes. • Must be easily available.
Bacterial water analysis • Is a routine check to make sure that the concentration of potentially pathogenic bacteria in drinking water is sufficiently low to say it is safe for human consumption. • Three indicator bacteria are chosen: non-specific coliforms, Escherichia coli and Pseudomonas aeruginosa. • Coliforms (esp. E. Coli) could suggest the possibility of fecal matter contamination of a water supply. • Coliform Index is usually given as a measure of human fecal matter in the water.
Escherichia coli • Escherichia coli is an indicator bacteria. Its presence in water supply could suggest the possibility of faecal matter contamination of a water supply. Such water cannot be used for drinking
Drinking water purification • Is removal of contaminants from raw water to produce drinking water that is pure enough for human consumption or for industrial use. • Substances that are removed are: parasites (Giardia, Cryptosporidium), bacteria, algae, viruses, fungi, minerals (lead, copper), man-made chemical pollutants.
Sources of drinking water • Deep groundwater-is generally of very high biological quality, but may be rich in dissolved solids, especially carbonates, sulphates of calcium and magnesium. • Shallow groundwater is usually abstracted from wells or boreholes. Its’ bacteriological quality is variable. A variety of soluble material may be present in it. • Upland lakes and reservoirs-bacteria and pathogen levels are usually low.
Sources of drinking water • Rivers, canals and low land reservoirs-will have a significant bacterial load. • Atmospheric water generation- is a new technology that can provide high quality drinking water by extracting water from air by condensing water vapour. • Rainwater harvesting or fog collection- can be used in areas especially with significantly dry seasons.
Water treatment • Primary treatment- collecting, screening and initial storage. • Secondary treatment- removal of fine solids and the majority of contaminants using filters, coagulation, flocculation and membranes. • Tertiary treatment-polishing, pH adjustment, carbon treatment to remove taste and smell, disinfection, and temporary storage.
Water disinfection • Means destroying any living pathogens (viruses, bacteria including E. coli, Campylobacter, Shigella, protozoans including Giardia lamblia and Cryptosporidia).
Means used for water disinfection • Chlorine- the most commonly used. A major drawback to using chlorine is that it reacts with organic compounds in the water to form potentially harmful trihalomethanes (THMs) and haloacetic acids, both of which are carcinogenic. • Chlorine dioxide • Chloramines • Ozone • UV radiation
Water treatment options • Fluoridation to prevent tooth decay. • Water conditioning to reduce the effects of hard water. Water hardness is content of calcium and magnesium carbonate dissolved in it. • Plumbo- solvency reduction- in some locations water is capable of dissolving lead from any lead pipes that it is carried in. Lead is toxic. • Radium removal. • Fluoride removal.
Other water purification techniques • Boiling for three minutes to disinfect water. • Charcoal filtering allows to remove many compounds including toxins. • Distillation -involves boiling to produce vapour and then condensing it. Distillation does not completely purify water. The distillation apparatus may be the ideal place to harbour Legionella .
Wastewater • Is any water that has been adversely affected in quality by antropogenic influence. It comprises liquid waste discharged by domestic residences, commercial properties, industry and agriculture .
Sewage • is the subset of wastewater that is contaminated with faeces or urine.
Wastewater constituents • Water >95%. • Pathogens: bacteria, viruses, prions, parasites. • Non- pathogenic bacteria. • Organic particles (faeces, hairs, food, paper, plant material). • Soluble organic material (urea, fruit sugars, protein, drugs). • Inorganic particles ( sand, metal particles, ceramics).
Wastewater constituents • Soluble inorganic material (ammonia, road-salt, cyanide, hydrogen sulphide). • Animals (protozoa, insects, arthropods, small fish). • Macro-solids (sanitary towels, diapers, condoms). • Gases (hydrogen sulphide, carbon dioxide and methane). • Emulsions (paint, adhesives, mayonnaise). • Toxins (pesticides, poisons).
Biochemical Oxygen Demand (BOD) • Is a wastewater quality indicator. • Any oxidizable material present in a natural waterway or in an industrial wastewater will be oxidized by both biochemical (bacterial) or chemical processes. The result is that the oxygen content of the water will decrease • Oxidizable material+ bacteria+ nutrient +O2-› CO2+ H2O+ oxidized inorganics such as NO3 or SO4.
Chemical Oxygen Demand (COD) • Oxidizable chemicals (such as reducing chemicals) introduced into a natural water will initiate chemical reactions. Those chemical reactions create what is measured as Chemical Oxygen Demand. • Both BOD and COD tests are a measure of relative oxygen-depletion effect of a waste contaminant. Both have been widely adopted as a measure of pollution effect.
5-day BOD • Measures the amount of oxygen consumed by biochemical oxidation of waste contaminants in a 5-day period.
Oxidizable chemicals (such as reducing chemicals) introduced into a natural water will initiate chemical reactions. Those chemical reactions create what is measured as Chemical Oxygen Demand. • Both BOD and COD tests are a measure of relative oxygen-depletion effect of a waste contaminant. Both have been widely adopted as a measure of pollution effect.
Wastewater treatment • Most wastewater is treated in wastewater treatment plants which include physical, chemical and biological treatment processes.
Wastewater reuse • Treated wastewater can be reused as drinking water (Singapore), • in industry (cooling towers), • in artificial recharge of aquifiers, • in agriculture (70% of Israel’s irrigated agriculture is based on highly purified wastewater), • in rehabilitation of natural ecosystems (Florida’s Everglades).